Solder melting pot



Feb. 1940- J. D. MORGAN ET AL SOLDER MELTING POT Filed July 17, 1935 INVENTO JOHN D. ORG N BY RD ELL E.

o 3 2 W a ATTORN EY Patented Feb. 13, 1940 UNITED STATES PATENT OFFICE SOLDER MELTING POT poration of Maine Application July 17, 1936, Serial No. 91,137

3 Claims.

This invention relates generally to electric heating apparatus and is more particularly directed to an improved solder melting pot having an electric heater attachment and process of making same.

Among the objects of the present invention are: to provide an improved solder melting pot and electric heating element therefor; to provide an electrie heating element for a metal pot in which the electric resistor filament is embedded in a dielectric refractory body of high thermal conductivity mounted immediately beneath the bottom of the pot and supporting the filament in ::paced electrically insulated relation thereto; to

ll provide a process for assembling a solder melting pot and an electric heater attachment therefor whereby the heating element is cast in place into a unitary bonded structure with the pot, without adverse effect on'the strength or elecn trical conductivity of the fragile resistor fi1ament; to provide an improved method for forming a mechanically strong and highly heat con-` ductant junction between an end of a fragile electric resistor filament and a metal terminal post.

With the aforementioned objects and other objects and features in view, the invention consists in the improved solder melting pot and process of manufacturing same which is hereinafter described and particularly deflned by the accompanying claims.

The invention will be herenafter more particularly described by reference to the accompanying drawing which illustrates in a vertical sectional View a solder melting pot incorporating the invention which forms the subject of the present application.

Referring to the drawing, it will be seen that the principal parts of the solder melting pot therein illustrated include a steel pot o, to the outer peripheral wall of which there is affixed a cylindrical sheet metal skirt !2. The lower end of the skirt l2 extends a considerable distance below the bottom of pot n, and between the inner walls of the skirt l2, and aflixed thereto as well as to the bottom of the pot n, is an electrical resistor heating element l4. Heating element |4 is made up of a coil of high temperature resistant alloy metal filament IS embedded in a highly heat conductant dielectric body of refractory. The two ends l8--20, of the filament IS, are illustrated as extending downwardly a short distance below the resistor |4 and as being connected by fused metal joints 22 to metal terminal posts 24. Each of the junctions 22 between the filament ends s and and the posts 24 is provided with a protective highly heat conductant sleeve 26 comprising a cylirder of thermally conductant dielectric refractory cast in place around the joint and that portion of the filament ends I8-20 and terminal posts 24 contiguous to the joint. The solder melt 5' ing pot illustrated also includes a metal plate 28 forming a closure for the lower end of skirt !2, and a sheet metal casing 30 having supporting legs 32. The spaces between casing 30 and skirt 12, and between the bottom of the casing and 10 the resistor i 4 are filled with heat insulating material 33 such as magnesia or magnesia-asbestos mixture.

In assembling the pot which is illustrated in the drawing, the first step is to turn the pot o 16 upside down and to attach thereto by spot weld the sheet metal skirt |2 having an inner periphery dimensioned to tightly fit the outer peripheryof the side walls of pot o. The next step is to build up a layer 34 of a plastic mixture of refraczo tory material on the bottom of pot !2 in the manner indicated, and to allow this layer to harden. A preferred refractory for this purpose is the zircon-ferro-silicon refractory which is deseribed in our copending application Serial No. 25:.

87,662, filed June 27th, 1936, for High temperature refractory. This refractory is best prepared by admixing to parts by Weight of milled grain zircon (through 300 mesh) with 50 to parts of silicon or %-85% ferro-silicon 30 (through mesh) and not substantially more than one part of aluminum hydrate (through 100 mesh). The aforesaid mixture is prepared for spreading on the base of the pot by wetting to the proper consistency with water and with 35 orthophosphoric acid employed as a binding agent in the proportions of about 6 cc. per grams of the silicon-zircon-aluminum hydrate mixture. After applying the layer 34 of the plastic mixture of refractory material in a dampened state, it is w air dried and the metal lament !6 is then laid on the layer 34 in the form of a helical coil. The coil should be previously laid out in loops and shaped to the curvature of 'the exposed surface of layer 34 and set so as to prevent short circuiting between successive loops of the coil, by an annealing operation. The preferred material for the coil IS is chromium (about 35%)-iron-aluminum (about 7%) alloy wire which Will stand up under temperatures of the order of 2300 F. 20 gauge wire is a suitable size for the filament. After placing the coil IB, another layer 36 of the same type of thermally conductant electrically nonconductant refractory mixture is built up on the layer 34, thus embedding the coil in the refracw tory resistor HI of approxmately the shape indicated. The free ends 18 and 20 of the resistor filament are then attached to heavy metal terminal posts 24 by a high temperature arc fusion or welding operation to form the fused metal joints 22. suitable rnolds are then inserted over the posts 24 and the high temperature refractory sleeves 2 6 are formed by'pouring thesemolds full of a plasticmixture ofphosphoricacid and zircon-silicon ref'actory material, and allowing the mixture to air dry.

After casting and air drying the resistor IL v pot. Conductors ti? are attached to the terminal posts 24 for supplying current from any source (hot shown) to the heating element.

As previously indicated, the filament !E is pre-- erably constructed of a fragile metal alloy such as a high chrome-iron-aluminum alloy adapted to Wlthstand high temperatures. Likewise the 'terminal posts 24 are preferably constructed of an alloy of the type of heavynichrome. The refractory ptotective sleeves 26 ior the joints 22 connecting the `ende of the resistor flament With the heavy nichrome terminals are a very important feature of the invention, since it is apparently only by the use of these highly heat conductant and electrically non conductant protective sleeves ofbondedzircon-siliconrefractory that a mechan- ;ically strong and non-deteriorating joint can be made between such a fragile metal alloy filament and a heavy terminal post of a nichrome or the like. One function of the sleeves 25 is to serve as heat radiating elements for rapid distribution of any heat developed at the joints 22, and thereby provide a relatively cool joint between the nichrome terminal post and the chrome-ironaluininum Wire.

The invention having been thus described; what is claimed as new isi 1. A solder melting pot, oomprising' a pot shaped metal container for holding the solder, a sheet metal skirt surrounding and coniorming to the lower portion of the container and extending downwardly a substantial distance therebelow, an. electrical heating unit intimately bonded to the bottom wall of thescontainer within the extended portion of said skrt, said' heating element com prising a metallic electric resistance heating filai ment embedded directly in heat conducting electric insulating refractory material containing a substantial proportion of ferro-silicon, Whereby heat produced by said filament is rapidly cony ducted` to the'bottom of said container.

2. A solder melting pot as defined by claim 1 in which the ends of 'said heating lament are used to metal. terminalsfor supplying electric current to the filament and in which the resulting fused joints are embedded in electrically insulating 'finely divided zircon, a substantial portion of finely divided ferrosilicon and a relatively small portion of phosphoric acid on the bottom of the container within the skirt, placing an electrical resistance heating element on said layer, orming another layer of said plastic refractory material over said heating element and said first-mentioned layer to embed the element, said mixture of refractory material being adapted whenbaked to provide an electrical insulating refractory of high heat conductivity, and baking said refractory assembly at a temperature suicient to intimately bond the refractory .material as a unit and to unite the refractory material to the container whereby an electrical heating element is bonded directly to the bottom of the container.

JOHN e. MORGAN; RUSSELL E. LOWE.

siti. 

